Spectroscopy

Quantum mechanics

Spin (aerodynamics)

Ground state

Antiferromagnetism

Proton

Nuclear structure

Nuclear physics

Atomic physics

Radiative transfer

Thermodynamics

Hydrogen

Physics

Hyperfine structure

Nucleon

Exotic atom

Electron

Lamb shift

Spin structure

Annual Review of Nuclear and Particle Science

Laser spectroscopy of muonic atoms has been recently used to probe properties of light nuclei with unprecedented precision. We introduce nuclear effects in hydrogen-like atoms, nucleon structure quantities (form factors, structure functions, polarizabilities), and their effects in the Lamb shift and hyperfine splitting (HFS) of muonic hydrogen (μH). Updated theory predictions for the Lamb shift and HFS in μH are presented. We review the challenges of the ongoing effort to measure the ground-state HFS in μH and its impact on our understanding of the nucleon spin structure. To narrow down this search, we present a novel theory prediction obtained by scaling the measured HFS in hydrogen while leveraging radiative corrections. We also summarize recent developments in the spectroscopy of simple atomic and molecular systems and emphasize how they allow for precise determinations of fundamental constants, bound-state QED tests, and New Physics searches.

The Proton Structure in and out of Muonic Hydrogen